Hach sension6, Instruction Manual, Page: 39 / 86

38
SECTION 3,
continued
With the probe in the calibration and storage chamber, observe
the mg/L dissolved oxygen concentration after the probe has been
polarized for the appropriate period of time. Calibration may be
performed when the display is stable for several minutes.
3.3.3 Zeroing the Probe
Zeroing the sens
ion
6 Dissolved Oxygen meter is necessary only
when measuring dissolved oxygen levels less than 1 mg/L or 10%
saturation. A new DO probe can generate a 0.02 to 0.05 mg/L
positive error in an oxygen-free (anoxic) solution. If this level of
error cannot be tolerated, zero the meter using the following
procedure. Also conduct this zeroing procedure after replacing
the sensing membrane or changing the internal filling solution.
1. Measure about 150 mL of sample or deionized water into a
250-mL beaker. Add a magnetic stir bar.
2. Add 0.25 g sodium sulfite or the contents of one Silica 3
Reagent Powder Pillow to the water. Stir to dissolve
the reagent.
3. Catalyze the reduction of dissolved oxygen by adding 0.1 mL
of a 1000 mg/L Cobalt Standard solution to the water.
4. Place the probe in the stirring sample for at least 10 minutes.
This solution is good for 30 minutes or more.
5. Press the
CAL
key. The Cal icon will appear in the upper left
corner of the display, a flashing question mark will appear in
the upper right corner of the display, and the keypad icon will
appear in the lower left corner of the display.
6. Press the
READ ENTER
key three times to skip to the display
showing
100%
.
7. Press the
0
key on the keypad then press
READ ENTER
.
8. The meter shows
Stabilizing...
while readings are taken. When
the meter’s zero DO criteria have been met it will return to
the read mode. The meter will not exit the zeroing routine
until the meter’s zero criteria have been met.